PNW
Pacific Northwest
Research Station
I n s i d e
Expediting Old Growth .............................................2
Working in the Zone ..................................................3
Cool and Moist ..........................................................4
Reserve Design ..........................................................5
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issue ninety nine / january 2008
“Science affects the way we think together.”
Lewis Thomas
SAVING STREAMS AT THEIR SOURCE: MANAGING FOR
AMPHIBIAN DIVERSITY IN HEADWATER FORESTS
IN
S U M M A R Y
Although stream protection has become a
central tenet of forest management in the
Pacific Northwest, it is often only the larger,
fish-bearing streams that are afforded the
strongest safeguards. Yet, even without fish,
headwater streams and riparian areas are
hotspots of biodiversity, and they are the source
of much of the water, gravel, and nutrients
that subsidize downstream environments.
Amphibians, in particular, thrive in the
relatively cool and moist microclimate created
by headwater streams. In fact, more than a
quarter of amphibian species in the region
have life histories reliant on headwaters.
Headwaters make up more than 75 percent of the total stream network, yet regulatory protections
are often weaker within headwaters owing to their lack of fish.
“To protect your rivers,
protect your mountains.”
F
—Emperor Yu of China
orest managers have long understood the importance of protecting
streams and their adjacent riparian areas. Indeed, stream buffers are the
cornerstone of most strategies to safeguard
forest biodiversity, water quality, and
ecological integrity. And although nearly
everyone agrees that stream protection is
important, there is no consensus on exactly
what constitutes a stream—at least in
regulatory terms. Many forest policies only
afford protection to streams that support
fish. However, new research is expanding
our perspective beyond this fish-centric
view and suggesting a need for alternative
management designs for upstream
headwater riparian areas.
By definition, headwater streams are
small, usually less than 6 feet across.
But what they lack in width they make
up for in length: more than 75 percent
of the total stream network is headwater
streams. They are the source of much of
the water, gravel, wood, and nutrients
that flow through the stream network
and eventually to the ocean. Owing to
favorable microclimate and availability of
water, headwaters provide habitat for distinct assemblages of plants and animals.
“Headwater streams and riparian
areas are a nexus of biodiversity, with
disproportionate numbers of species
tied to this habitat,” says Dede Olson,
Scientists working on the Density Management
and Riparian Buffer study recently completed
the first phase of research into the effectiveness
of riparian buffers as habitat reserves in
headwater forests. They found that even when
using the narrowest riparian buffer (20 feet),
thinning upslope did not adversely affect
headwater amphibian populations; slightly wider
buffers (approximately 50 to 75 feet) defined by
transitions from riparian to upslope vegetation
or by streamside topography were sufficient to
maintain headwater stream microclimates. In
some cases, abundances of upslope, terrestrial
salamanders were reduced within the region of
active thinning, but these impacts were small
and short-lived. This suggests that combined
stream buffers and upslope thinning may
effectively retain amphibian headwater habitat
and communities, and could aid in establishing
connectivity for terrestrially dispersing
amphibians across ridgelines and adjacent
headwater drainages.
a research ecologist at the PNW Research
Station in Corvallis, Oregon. “Nevertheless,
our knowledge of the ecology of these
systems remains sparse, even though they
are undergoing widespread degradation at
alarming rates.”
Headwater streams are distinct from their
downstream counterparts in many ways.
“Tightly constraining valley walls and
riparian vegetation often shade the full
width of headwater streams,” explains
Paul Anderson, a research forester at the
PNW lab in Corvallis. “This contributes to
microclimates that are unique to headwaters
and that influence stream temperatures and
habitat for terrestrial and aquatic organisms.”
Some headwater streams are seasonally intermittent, running dry in the heat of the summer. Others periodically flow underground
into the “hyporheic zone” before resurfacing
further downstream. These features, along
with frequent cascades and obstacles, explain
the lack of fish, which turns out to be a boon
for some amphibians, such as torrent salamanders, that thrive in fishless headwaters.
Amphibians, in general, seem to flourish
in headwater streams and forests. All 47
Northwestern amphibian species have stream-
K EY FINDING S
• Unique amphibian assemblages occur in headwater streams of managed forests in
western Oregon, with some species having close ties to stream hydrology patterns
such as spatially intermittent reaches.
• Instream and bank amphibians in headwaters of managed forests were not adversely
affected by upslope thinning to 80 trees per acre when riparian buffers 20 to 450 feet
wide were retained adjacent to streams.
• Abundances of terrestrial salamanders occurring from banks to uplands were reduced
after thinning in some cases, and not in others. Site-specific conditions appear to
be linked to their responses, where habitat features such as legacy down wood or
occurrence of rocky substrates at sites may ameliorate effects of overstory removal.
riparian associations, and a quarter of those
have life histories reliant on headwaters in
particular. Because amphibians require cool,
moist microclimates and often divide their
life history between the stream and upslope
forests, they can be quite sensitive to forest
disturbances, particularly logging. According
to Olson, monitoring the status of amphibian
populations may be an effective barometer for
estimating the impacts of forest management
on ecosystem integrity. She is now involved in
a study that puts that theory to the test.
Olson and Anderson are investigators in a
large, multidisciplinary study that is quantifying ecosystem effects of novel types of
forest management in headwater forests: The
Density Management and Riparian Buffer
study. They recently completed the first phase
of research, which documented the efficacy
of headwater riparian buffers for maintaining
microclimate and amphibian populations in
association with thinning projects designed to
restore old-growth forests on federal lands.
Ex pediting old growth
F
rom the 1950s until the 1980s, the
Forest Service and Bureau of Land
Management (BLM) clearcut Douglasfir forests at a rate unimaginable on federal
lands today. This was before the spotted-owl
controversy, during a time when old-growth
forests were commonly viewed as decadent
and rotting. Many headwater forests were
cutover during this period. Often, the streams
themselves were used as flumes to transport
the logs out of the forest. Today, the legacy of
those harvests is evident within hundreds of
thousands of acres of young, dense, even-aged
forests, all between 25 and 60 years old.
Clearly times have changed, and restoring old
growth has become the management directive
de jour. The challenge managers face now
Purpose of PNW Science Findings
To provide scientific information to people
who make and influence decisions about
managing land.
Kathryn Ronnenberg
PNW Science Findings is published
monthly by:
Pacific Northwest Research Station
USDA Forest Service
P.O. Box 3890
Portland, Oregon 97208
Send new subscriptions and change of address
information to pnw_pnwpubs@fs.fed.us
The Density Management and Riparian Buffer study was designed to test the effectiveness of different
buffer widths for protecting amphibian assemblages and microclimate around headwater streams while
thinning harvests were conducted upslope.
Science Findings is online at: http://www.fs.fed.us/pnw/
The site includes Science Update—scientific knowledge for pressing decisions
about controversial natural resource and environmental issues.
Sherri Richardson-Dodge, editor
srichardsondodge@fs.fed.us
Keith Routman, layout
kroutman@fs.fed.us
United States
Department
of Agriculture
Forest
Service
2
is learning how to expedite the development
of old-growth conditions from plantations.
Time is obviously one key ingredient, but
dense young forests left to their own devices
do not readily transform into structurally
diverse old growth. Aggressive thinning is
seen as the pathway to restoration. Thinning
opens the canopy, freeing up sunlight and
other resources, which increases growth in
the remaining trees while also allowing an
understory canopy to establish.
The Density Management and Riparian Buffer
study was designed to test the ability of thinning to produce old-growth characteristics
while also minimizing ecological impacts of
harvest operations. Study sites were primarily
on forests managed by the BLM distributed
throughout the Oregon Coast Range and
Oregon Cascade Range.
“The thinning in our study was originally
viewed as aggressive,” says Anderson. “Our
objective was to open the canopy enough to
allow sufficient light to spur tree regeneration and so that it stayed open until those
trees become established. Twenty years ago,
thinning from 200 trees per acre down to 100
would have been considered a heavy thinning.
For our objectives we thinned to 80 trees per
acre—and that might not even be enough.
It’ll only be 8 to 10 years before the overstory
canopy closes back up.”
Thinning was used to lower the density of second-growth forests from over 200 trees per acre down to
about 80. This will accelerate growth in the remaining Douglas-fir trees and promote new understory
canopy.
and left several ¼- to 1-acre retention islands,
all in an effort to maximize forest stand
heterogeneity.
Loggers left the largest trees and thinned the
rest in a nonuniform pattern. Canopy cover
was no less than 40 percent after harvest.
They also cut several ¼- to 1-acre patches
The study was designed to test four riparian
buffer widths wherein no cutting was allowed.
The buffers corresponded to the range of
current federal and state forest practices and
ranged from 20 to 475 feet, on each side of
the stream. One treatment had variable buffer
widths depending on site-specific boundaries
between riparian and upslope topography and
vegetation; this strategy mimics recent practices on federally owned headwater forests.
Working in the zone
O
The headwaters lived up to their reputation as amphibian hot spots. All told, the
researchers captured and released more than
3,000 individuals representing 13 amphibian species. The coastal giant salamander,
Dunn’s salamander, western red-backed
salamander, and torrent salamander were,
by far, the most frequent captures.
Kathryn Ronnenberg
lson and several colleagues sampled
amphibian abundances and diversity along 68 headwater streams
throughout 11 thinning sites—carefully
searching under cover items such as rocks
and logs in streambeds and along streambanks, and in upland transects at a couple
of case study sites. They sampled one year
before and two consecutive years after the
thinning. “They are cryptic animals and we
survey during the wet spring when they are
most active at the ground surface,” explains
Olson. “Some amphibians go subsurface in
the summer, and may or may not emerge
again in the fall when it rains.”
Headwater stream
drainages showed
differences in amphibian
assemblages, both with
streamflow regime and
distance into uplands, as
shown by pie diagrams
with different wedges
representing the relative
abundance of different
species. In this diagram,
“A” indicates the area
of the “stream effect”
where microclimates are
affected by streams, and
“B” indicates the upland
edge effect from forest
management activities.
“C” indicates a different
amphibian assemblage
occurring in spatially
intermittent streams,
compared to perennially
flowing water downstream,
where torrent salamanders
(white edge) are frequently
found.
3
“I was disappointed that we didn’t find
more tailed frogs,” says Olson. “They are
listed as a sensitive species in the region and
don’t seem to do as well in these managed
forests.”
“Overall, I think the thinning was a rather
benign disturbance from an amphibian point
of view,” she adds.
William Leonard
The good news is that the harvesting
operations had little impact on amphibian
populations. “Instream- and bank-dwelling
amphibians were not adversely affected by
the thinning upslope,” says Olson. “In some
cases, abundances of upslope, terrestrial
salamanders were reduced within the region
of the active thinning, but these reductions
were small and short-lived.”
Southern torrent salamanders were associated with spatially intermittent headwater streams, and are a
species of concern in the region.
Cool and moist
‘‘I
n riparian areas, open water surfaces,
moist soils, and abundant vegetation
contribute to the formation of unique
microclimatic conditions that extend laterally
from streams,” explains Anderson. “The
streams create a distinct local environment
through influences on air temperature and
humidity. This is what we call the stream
effect, and it can have a pronounced effect
on riparian plants and wildlife.”
“The Density Management study allowed us
to examine the stream effect within headwater
systems, where it has received less attention,”
says Anderson, who tested whether riparian
buffers of varying width could effectively
maintain the stream effect, even in the face
of aggressive thinning immediately upslope.
Using electronic data loggers, researchers
recorded temperature and relative humidity
along transects from stream center upslope
into the thinned stands, patch openings, and
unthinned forest. As expected, temperature
increased with distance from the stream,
whether or not there was thinning upslope.
The stream effect was greatest within 30
feet of the stream; beyond that, temperatures
increased at a lesser rate. Relative humidity followed the same general pattern but
decreased with distance from stream.
Thinning increased temperature and reduced
humidity upslope within the harvest area,
but with variable-width or wider buffers,
the harvest had only subtle influence on the
microclimate around the stream. In fact, the
average air temperature at stream center was
less than 1 degree greater than in unthinned
stands. According to Olson, that’s well within
the tolerance of most amphibians.
Kathryn Ronnenberg
“The changes we saw represent the absolute
maximum effect on microclimate. We took
our measurements at the hottest time of day
during the warmest summer months. The
microclimatic influence of these thinnings
during spring, when amphibians are surface
active, would likely be much less.”
Retention of the “stream effect” on microclimate may be a consideration of headwater stream-riparian
management. In this diagram, “A” indicates the area of the “stream effect” where microclimates are
affected by streams. “B” indicates the edge effect from upland thinning outside of riparian buffers on
streams. The vertical dashed line shows where the steep gradient of the stream effect begins to moderate.
W R I T ER’ S PROF I LE
Jonathan Thompson is an ecologist and science writer. He lives in Corvallis, Oregon.
4
R eserve design
L A ND M A N AG E M ENT I M PLIC A TIONS
A
ll the thinning treatments included
in this study thus far incorporated a
riparian buffer, and even the narrowest of these—just 20 feet across—effectively
protected amphibian populations. The next
phase of research will evaluate the impact of
thinning across the headwater streams themselves. “We certainly wouldn’t have moved on
to phase two, had we gotten different results
in phase one,” says Olson.
• Stream buffers in thinned stands may effectively retain amphibian headwater habitat
and communities, and could aid in connecting amphibian habitat across ridgelines
and adjacent headwater drainages.
• Retention of legacy down wood and active management for recruitment of down wood
in managed stands may be beneficial to ground-dwelling terrestrial salamanders.
• Riparian buffers of various widths can be used to moderate changes to riparian and
above-stream microclimates when timber harvest occurs in adjacent headwater forests.
Understanding the full range of impacts associated with thinning will help forest policymakers develop more effective regulations for
managing headwater riparian forest. Whereas
protection standards for fish-bearing streams
are relatively consistent and robust across all
ownerships, protections for non-fish-bearing
streams differ widely.
FOR F U RT H ER R EA DI NG
Anderson, P.D.; Larson, D.J.; Chan, S.S.
2007. Riparian buffer and density management influences on microclimate of young
headwater forests of western Oregon.
Forest Science. 53(2): 254–269.
Since 1994, when the region’s federal forests
came under the jurisdiction of the Northwest
Forest Plan, fishless headwater streams have
been protected by a buffer one tree height
wide, although narrower buffers are often
used after site-specific conditions have been
assessed. On state and private lands in Oregon
and Washington, small headwater streams
have no required buffers at all.
“Connectivity of habitat, both longitudinally
along streams and laterally away from streams
into uplands, is also important for long-term
persistence of headwater amphibian species
and assemblages,” she adds. “Amphibians are
surprisingly mobile, and in order for populations to persist over the long term, there needs
to be linkages connecting adjacent headwater
streams. This means extending some of the
buffers protecting adjacent headwater streams
up to the ridgeline where they would connect.”
Reserve designs that explicitly incorporate
landscape connectivity in headwater forests
result in what Olson calls the “spaghetti and
meatballs design.” On a map, it’s easy to see
why: long, narrow buffer strips run parallel
to the streams (the spaghetti) protecting
instream- and bank-dwelling species while
also preserving the “stream effect” on
microclimate. Near the ridgetop, or adjacent
Kathryn Ronnenberg
Although Olson and Anderson hesitate to
make specific management recommendations,
they have outlined some features of a headwater protection strategy that they believe
are important. “A reserve system should be
designed to retain all habitats used by target
species of amphibians, recognizing their
complex life histories that bridge aquatic and
terrestrial habitats. These include a mix of
riparian and upslope management approaches
to address the breeding, foraging, overwintering, and dispersal functions of these animals,”
says Olson.
Olson, D.H.; Anderson, P.D.; Frissell,
C.A.; Welsh, H.H., Jr., Bradford, D.F. 2007.
Biodiversity management approaches for
stream riparian areas: perspectives for
Pacific Northwest headwater forests,
microclimate and amphibians. Forest
Ecology and Management. 246(1): 81–107.
Olson, D.H.; Rugger, C. 2007. Preliminary
study of the effects of headwater riparian
reserves with upslope thinning on stream
habitats and amphibians in western Oregon.
Forest Science. 53(2): 331–342.
Headwater reserve designs for riparian
management to retain amphibian communities
include a “spaghetti and meatball” approach,
with stream buffers of different widths as
spaghetti and patch reserves in different
configurations as meatballs to provide
connectivity among streams over ridgelines.
to the streams, protected patches (the
meatballs) may connect habitat and allow
individuals to move across the landscape.
Olson, D.H.; Weaver, G. 2007. Vertebrate
assemblages associated with headwater
hydrology in western Oregon managed
forests. Forest Science. 53(2): 343–355.
Rundio, D.E.; Olson, D.H. 2007. Influence
of headwater site conditions and riparian
buffers on terrestrial salamander response
to forest thinning. Forest Science. 53(2):
320–330.
According to the researchers, more research is
needed into different strategies for protecting
headwater forests in the face of thinning and
other types of forest management. For now,
simply acknowledging that small, non-fishbearing streams are an important ecological
resource deserving protection is a big step in
the right direction.
“Water is the most critical
resource issue of our lifetime
and our children’s lifetime.
The health of our waters is
the principal measure of
how we live on the land.”
—Luna Leopold
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PRSRT STD
US POSTAGE
PAID
PORTLAND OR
PERMIT N0 G-40
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U.S. Department of Agriculture
Pacific Northwest Research Station
333 SW First Avenue
P.O. Box 3890
Portland, OR 97208-3890
Official Business
Penalty for Private Use, $300
scientist profileS
DEANNA OLSON
is a research
ecologist with
the Aquatic and
Land Interactions
Program at the
USDA Forest
Service, Pacific
Northwest
Research Station. She co-leads the
Aquatic and Land Interactions Team in
Corvallis, Oregon. Olson has a Ph.D. in
zoology from Oregon State University
and a B.A. in biology from the University
of California, San Diego. Her research
is largely focused on the ecology of
aquatic-riparian-dependent animals such
as amphibians, with specific emphasis
on examining the effects of forest
management practices. Recent work
includes development of rare species
conservation guidance.
PAUL ANDERSON
is a supervisory
research forester
with the Resource
Management and
Productivity Program
at the USDA Forest
Service, Pacific
Northwest Research
Station. He is the leader of the Biology and
Culture of Forest Plants Team in Corvallis,
Oregon. Anderson has a Ph.D. in wildland
resource science from the University of
California, Berkeley, an M.S. in forest
resources from Purdue University, and a
B.S. in forest resource management from
the University of Minnesota. His current
research projects address silviculture
of young forests, riparian silviculture,
physiological and genetic bases of
productivity, postfire restoration,
and genecology of white pine.
Olson and Anderson can be reached at:
Pacific Northwest Research Station/
USDA Forest Service
Forestry Sciences Laboratory
3200 SW Jefferson Way
Corvallis, Oregon 97331
Olson:
Phone: (541) 750-7373
E-mail: dedeolson@fs.fed.us
Anderson:
Phone: (541) 758-7786
E-mail: pdanderson@fs.fed.us
COOPER ATORS
Chris Sheridan, Bureau of Land Management
Klaus Puettmann and John Tappeiner,
Oregon State University
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